A. Technical Field
This invention relates generally to semiconductor manufacturing and packaging and more specifically to semiconductor manufacturing in MEMS (Microelectromechanical systems) sensing products.
B. Background of the Invention
MEMS sensing products can fail as a result of stresses and external mechanical shock such as rock impingement. For critical applications this can have catastrophic consequences. One field for which the consequences are catastrophic is in the field of automotive stability control, automotive air bag systems is another field and engine pressure management is yet another field for which consequences are catastrophic.
Automobiles use an inertial sensing device or a gyroscope device to assist in stability control and roll-over detection. The proper operation of the gyroscopic device is critical to the safety of the passengers of the automobile in order to detect a potentially dangerous condition, such as loss of control or roll-over. The gyroscope device normally is under a car within a housing. The location of the gyroscope device makes it particularly prone to impact by debris from the road. Even within the housing a rock, pebble or other road debris can impact the housing of the gyroscopic device and impair its operation.
Under normal conditions, the gyroscope has a drive mass that operates at a high frequency (typically approximately 10-50 KHz). The control of this frequency is critical in achieving the sensitivity specification and therefore this frequency is controlled by a closed loop system. When a pebble or rock strikes the gyroscope housing, it may generate a shock frequency that is at a resonant mode of the gyroscope system. This impact will then cause the drive mass to touch the substrate resulting in a loss of lock on the drive signal. This impact causes a brief failure of the gyroscope device. However, that brief failure can occur at a critical time and by the time the gyroscope device has recovered the vehicle could have already rolled over.
Unfortunately, the functioning of the gyroscope device is even more critical on road surfaces with a lot of debris, for example a dirt road or a road covered in pebbles. On those types of surfaces there are more likely to be stability control or roll-over issues. Also, those surfaces are more prone to impact and thus failure of the gyroscope device.
In summary, what is needed is a way to prevent the gyroscope device from failing due to impact.